The invention relates to a transfer device according to the preamble of claim 1 and a method for controlling a transfer device according to the preamble of claim 6.
It is in particular known in the mass production of punch or press parts to use multistage presses, wherein one workpiece is subsequently moved through the individual stations of the press at which a certain processing is performed. The workpieces are gripped at all stations of the press, lifted, transferred and transported to the next station by so-called transfer devices during the opening lift of the press. Accordingly, it is required that a transfer device normally performs a movement of the workpieces in three subsequently following vertical moving directions. Starting from an open position, which the transfer device assumes when the lift of the press was just completed, the transfer device must close. This usually means that so-called gripper rails extending in the travel direction of the workpiece are moved towards the workpieces from both sides thereof, and catching fingers, which are usually provided at the gripper rails will grip the workpieces. Then, the gripper rails, and, thus, the workpieces are lifted in order to move them out of mesh from the processing tools. Thereupon follows the feed of all workpieces in the travel direction of the press. When all workpieces have reached the correspondingly next processing station, the gripper rails and, thus, the workpieces are lowered. Finally, the grippe rails open and return to their starting position by a movement opposite to the direction of feed, so that a new further transfer of all workpieces may follow after the end of the lift of the presses.
U.S. Pat. No. 5,307,666 discloses a transfer device which performs a movement with only two axes. The workpieces are gripped by a movement of the gripper rails towards each other and transferred to the next station by a movement in the direction of feed. No lifting is provided therein.
According to U.S. Pat. No. 5,586,464, the workpieces are additionally lifted, with the closing movement as well as the lifting movement of the gripper rails being performed by a common driving apparatus and by means of a cam mechanism.
In U.S. Pat. No. 5,423,202, the closing and the lifting of the gripper rails is carried out by separate driving apparatus. However, the driving apparatus for closing the gripper rails is situated on that component part which is lifted by the lift drive. This has the deficiency that the lift drive must be designed comparatively large. Further, the electric cables and the like, which lead to the closing drive, must be moved in each lifting movement and are therefore subject to considerable wear.
These disadvantages likewisely apply to the subject matter of EP 0 701 872 A1, in which a lift drive is also provided in order to lift the gripper rails together with the drives for the closing movement.
According to EP 0 849 015 A2, a ball bearing spindle is provided for the movement in one of the two required directions. Such a ball bearing spindle is, on the one hand, very noisy in operation. On the other hand, very high driving speeds are required for the rotation of the ball spindle which makes a complicated design of the drive necessary.
These disadvantages also apply to the arrangement according to DE 197 21 613 A1, in which the gripper rail is supported on parallel steerings which are rotatably attached to a slide. By a further slide having a lever which acts on one of the parallel steerings through a nut connected to the further slide a lifting of the gripper rails is effected by the rotation of a spindle.
JP-A-06031358 discloses a drive of a gripper element which has toothed racks and pinions. Herein, the lift drive must also be moved with the close drive in the close direction. A lifting is performed by moving the lift drive which is suitably connected to the gripper element by additional pinions and toothed racks.
DE 39 33 775 A1 discloses a device according to the preamble of claim 1 and a method according to the preamble of claim 6. The close drive is performed by a fixed cam disk through a suitable crank gear. The drive of the lift is also performed by a cam disk through a crank gear which is connected to a rail which is transversely arranged. A vertical guide column is shiftable supported at the upper end of which the gripper elements are situated.
The invention is based on the objective problem to create a transfer device and a method for controlling a transfer device, wherein the arrangement of the transfer device and, in particular, of the required drives may be designed in a particularly simple manner.
The solution of this objective problem is realized by the transfer device according to claim 1.
Accordingly, a lift drive for lifting the gripper rail, which is generally designated gripper, is provided, on the one hand. On the other hand, the transfer device according to the invention has a close drive for moving the gripper in lateral direction. In addition, a controller is provided, which is required for the connection according to the invention of both drives with the elements to be moved, which is explained in the following.
According to the invention, both drives are namely fixedly mounted, so that none of the two motors must be designed such that it must also drive the respective other drive mechanism apart from the parts to be moved. It is in particular not required that the lift drive must inter alia lift the close drive. Consequently, the drives may be designed comparatively small and compact which means a first simplification of the transfer device according to the invention and the reduction of the manufacturing costs. In addition, this arrangement offers the advantage that the electrical cables and the like which lead to the drives do not need to be moved during normal operation so that they do not need to be designed excessively wear-resistant either, which means a further reduction of cost.
As was stated above, it is conceivable with fixed drives that the engagement with the elements to be moved is performed via ball bearing spindles which have, however, certain disadvantages. Further, it is known to realize the transmission of the motion of rotation of an electromotor into the translational movement of the gripper rail via toothed racks and toothed belts. However, those belts must have an extremely great cross section in order that they are not excessively extended when loaded. This is required for a sufficiently precise movement without risk of vibrations and the like. Finally it would be conceivable to connect the lift drive with the part to be moved by means of an element, which is shiftably provided on a drive element of the motor. In this case, the lift drive remains in engagement with the element to be lifted also during the opening and closing movement. However, such a construction is comparatively complex.
According to the invention, it is provided that the two drives are constantly in engagement with the parts to be moved in an exclusively articulated manner. No additional ball bearing spindle is therefore provided, as it is the case with DE 197 21 613 A1. Rather, according to the invention, the transmission of the motion of rotation of the motor into a translational movement of the elements to be moved is realized in that a comparatively simple lever and bracket mechanism is provided the elements of which are connected with each other in an exclusively articulated manner. The required translational movement is realized by means of a suitable guidance of the parts to be moved. The described exclusively articulated connection of the respective drive to the element to be moved is comparatively simple to realize and is a further contribution to the simplification of the construction.
It should be mentioned that in view of the described connection between the two drive motors and the elements to be moved a compensation must take place such that the gripper rail is, for example, not lowered when it is opened. Based on the fact that a plunger guided in a travel carriage, which is e.g. vertically liftable and realizes the lifting movement of the gripper rail, is in a lowered position when the gripper rail is opened, and because of the circumstance that the plunger is constantly in an articulated engagement with the lift motor, the drive of the plunger will be moved when the gripper rail is opened in such a manner that the connecting bracket describes a section of an orbit so that its front end lowers. By the controller in accordance with the invention the lift drive can in this case be operated by means of a path control such that it compensates the actually occurring lowering movement of the plunger, in other words, that it somewhat lifts the plunger relative to the travel carriage, so that the gripper rail, as is desired, remains on the same horizontal level. Consequently, a comparatively simply designed transfer device can be realized with the invention, which at the same time meets the requirements. Besides, the basic idea of the invention can be seen in that a fixed mounting of both drives becomes possible by the above-explained tracking of the one drive during the movement of the gripper in the direction of movement of the other drive. The transmission of the movement of the respective drive to the element to be moved can however also be performed in another manner than that described above.
Preferred embodiments of the invention are described in further claims.
In principle, the type of mounting of the gripper relative to a stationary base may be designed at will. However, it has proved to be advantageous to support the gripper in a vertical direction liftable in a travel carriage which may sideways be moved. In this case, the above-described compensation movement will result.
It is a considerable advantage for operating the transfer device according to the invention, if the gripper is resiliently supported relative to a stationary base. This resilient bearing may in principle be provided directly at the gripper rail. However, the bearing may also be provided between a stationary element on which the travel carriage is guided, and a stationary base. So, a so-called adjusting carriage which is stationary in normal operation and whereon the travel carriage is guided, may, for example, be resiliently supported relative to the stationary base. The resilient bearing is preferably realized by means of a biased spring. This type of bearing offers the advantage that in case of malfunction the drives will be loaded to a smaller extent. The control of the close drive is usually provided such that it is path-controlled. If now for whatsoever reason a collision occurs, e.g. since a workpiece was wrongly positioned in the press, the controller will detect that the close motor is not on the programmed path in view of the speed, which occurs if the gripper rail collides with an element. If the close motor leaves the predetermined xe2x80x9cwindowxe2x80x9d of its speed path, it will usually immediately be braked, which, however, represents a high load to the components involved. If, however, as is preferably provided, the gripper rail is resiliently supported, the close motor may remain for a certain time on the predetermined path since the resilient bearing takes to a certain degree over the movement of the gripper rail which was prevented by collision. The fact that the close motor, based on work xe2x80x9cagainstxe2x80x9d the spring,xe2x80x94needs more force than usually which indicates an accident, may be detected by suitable detecting mechanisms which are obvious to those skilled in the art. In this situation it is however not inevitably necessary to brake the motor rapidly down to zero speed, but due to the resilient support braking may be performed in a manner somewhat more smooth and gentle. It should be noted that a contact-less end switch may alternatively or additionally be provided in order to stop the motor when a certain shifting of the resilient bearing is reached, which operation may however also be performed in a comparatively gentle manner.
As stated above, it is preferred within the scope of the invention that the so-called travel carriage is moveable supported on an adjusting carriage, which adjusting carriage itself is adjustable provided on a stationary base. The position of the (closed) gripper relative to the workpieces may be adjusted by the adjusting carriage. In particular, the distance of the gripper rail in the closed state may be adjusted in the usually occurring case that the workpieces are gripped from two opposite sides by parallel gripper rails. This allows to adapt the transfer device to different workpiece dimensions in a flexible manner. The transfer device according to the invention is flexibly usable by the provision of an adjusting carriage. In addition, it is advantageous that cables and the like leading to the drives must be moved comparatively rarely, namely only in case of adjustment of the adjusting carriage, so that they do not need to be designed in an unnecessary robust manner as this would be the case when the cables needed to be moved in each cycle.
It is further preferred that a force compensating mechanism is assigned to the lift drive. The force compensating mechanism essentially acts in a way that it receives the weight force in the lifting movement, so that the lift mechanism is in equilibrium with respect to the static forces and must only take over the dynamic load, i.e. must essentially overcome the forces of inertia and friction. In addition, the gear of the motor is correspondingly relieved. Consequently, the force compensating mechanism further contributes to simplify the transfer device.
The solution of the above-indicated objective problem is further realized by the method described in claim 6.
Accordingly, a transfer device is operated by means of a controller such that at least one of the two drives is path-controlled during the movement caused by the other drive in such a way, that the element moved by one drive remains stationary in the direction of movement of said drive relative to the surroundings. In the case that the plunger, through which the lifting movement of the gripper is carried out, is supported in the travel carriage, by means of which the opening and closing movement of the gripper is realized, for example the lift drive is path-controlled when opened and closed in such a manner that the height level of the gripper remains unchanged. It is self-evidently also conceivable that a lifting carriage is moveably supported on a stationary element and a sideways shiftable element is supported in this lift carriage. In this case, the close drive should follow-up such that the lateral positioning of the grippers is not changed and the workpieces safely remain in engagement. The measure according of the invention allows to arrange the drives in a fixedly mounted manner and that they are exclusively articulated in mesh with the elements to be moved via a comparatively simple lever and bracket mechanism. Consequently, by the method according to the invention, a particularly simple transfer device can also be realized.
The basic idea of the invention may thus be seen in that two translational movements in different directions are performed by stationary drives provided independently of each other, with a movement in the second direction not being performed if a movement in the first direction is performed and vice versa. This is obtained, as was explained, by the path-controlled follow-up of the drive which is not to be activated at a certain time.
Preferred embodiments of the method of the invention are described in the further claims.
In accordance with the embodiment of the transfer device previously described as being preferred, it is preferred within the scope of the method according to the invention that the lift drive is that drive which follows-up in a path-controlled manner in order to correct an lowering or lifting occurred.
In accordance with the embodiment of the transfer device previously described, wherein a resilient bearing of the gripper relative to the stationary base is provided, it offers advantages in the method according to the invention, if the lift drive has a force measuring sensor which is connected to the controller, and the controller detects an accident when the measured force surpasses a threshold. Thereby it is possible, as explained above, that an accident is reliably detected and handled with comparatively simple means such that a braking of the drives is performed in a manner which results in an acceptable load on the components involved.